1. Field of the Invention
The present invention is directed to a mounting configuration and a mounting method of an optical waveguide holding member, and in particular to a mounting configuration and a mounting method of an optical waveguide holding member which has optical waveguides formed along a curved surface and allows an optical signal sent from the outside to be transmitted in a different direction.
2. Description of the Related Art
Due to the development of high-speed, high-capacity communications networks and communications controllers, fiber optic communications have become mainstream. For example, optical fibers are used to connect communications networks, such as the Internet, to information terminals and the like at home and at the office to transmit and receive signals. At the connecting part of a personal computer or a peripheral and an optical fiber (external optical fiber), an optical transceiver is provided to enable bidirectional conversion between an electrical signal and an optical signal. Such an optical transceiver includes an optical waveguide formed between the external optical fiber and a photoelectric conversion device (see Patent Document 1, for example).
[Patent Document 1] Japanese Laid-open Patent Application Publication No. 2005-115346
An optical transceiver like one described above has a structure in which an optical waveguide holding member having an optical waveguide is mounted on a printed circuit board on which a photoelectric conversion device is disposed. In general, the printed circuit board is made of glass epoxy resin, and the optical waveguide holding member is made of translucent olefinic resin. An optical path between the photoelectric conversion device on the printed circuit board and the optical waveguide on the optical waveguide holding member is connected by disposing a light receiving/emitting unit of the photoelectric conversion device to oppose a lens unit formed at the end of the optical waveguide in such a manner as to align their optical centers. The optical transceiver is required to bring the optical centers into alignment with a margin of position accuracy error of plus or minus several micrometers.
In the case where the printed circuit board is made of glass epoxy resin, the linear expansion coefficient of the printed circuit board is 13×10−6/° C. On the other hand, the optical waveguide has a linear expansion coefficient of 70×10−6/° C. Therefore, for example, if the optical waveguide holding member is mounted on the printed circuit board in an environment at an ordinary temperature of 25° C. and subsequently exposed to an atmosphere at 85° C. due to heat from peripheral devices, the photoelectric conversion device mounted on the printed circuit board is displaced by 10.007 mm, and the lens unit of the optical waveguide holding member opposing the light receiving/emitting unit of the photoelectric conversion device is displaced by 10.038 mm due to thermal expansion. In this case, the relative positional misalignment of the two is about 31 μm.
Conventionally, in order to reduce the relative positional misalignment between the lens unit of the optical waveguide holding member and the light receiving/emitting unit of the photoelectric conversion device due to thermal expansion, the optical axes are aligned in an atmosphere heated to a normal operating temperature of the optical transceiver during the assembly process of the optical transceiver, thereby reducing the misalignment of the optical axes due to thermal expansion.
However, this conventional production process leaves the problem that the production operation becomes complicated and desired position accuracy (inhibiting effect) cannot be obtained, thereby lowering process yield.
In the case where the optical centers of the light receiving/emitting unit of the photoelectric conversion device and the lens unit of the optical waveguide holding member are aligned by the motion control of a robot which automatically mounts the optical waveguide holding member on the printed circuit board, a two-stage adhesion process has been studied since the olefinic resin forming the optical waveguide holding member has weak adhesion. In the first stage of the adhesion process, a light curing adhesive is applied to a contact surface of the optical waveguide holding member, and the optical waveguide holding member is then mounted on the printed circuit board. In the second stage of the adhesion process, once the light curing adhesive hardens, a two-component mixed adhesive having firm adhesion is applied to the perimeter of the contact surface of the optical waveguide holding member in order to fix the optical waveguide holding member to the printed circuit board.
When the optical waveguide holding member is temporarily joined to the printed circuit board with the light curing adhesive after the placement by the robot motion control, the lens unit of the optical waveguide holding member and the light receiving/emitting unit of the photoelectric conversion device have their optical centers aligned to each other. However, unless the light curing adhesive is adequately applied, the optical waveguide holding member may be shifted in position from the fixing position at a time when the two-component mixed adhesive is applied. This results in a change in the relative position, and the lens unit of the optical waveguide holding member and the photoelectric conversion device on the printed circuit board therefore become out of alignment.